8.5. Summary
In this section, we learned more about the Debian package system, discussed the Advanced Pack-
age Tool (APT) and
dpkg
, learned about basic package interaction, advanced APT configuration
and usage, and dug deeper into the Debian package system with a brief reference of the
.deb
file
format. We looked at the
control
file, configuration scripts, checksums, and the
conffiles
file.
Summary Tips:
A Debian package is a compressed archive of a software application. It contains the application’s
files as well as other metadata including the names of the dependencies that the application needs
plus any scripts that enable the execution of commands at different stages in the package’s lifecy-
cle (installation, removal, upgrades).
The
dpkg
tool, contrary to
apt
and
apt-get
(of the APT family), has no knowledge of all the avail-
able packages that could be used to fulfill package dependencies. Thus, to manage Debian pack-
ages, you will likely use the latter tools as they are able to automatically resolve dependency issues.
You can use APT to install and remove applications, update packages, and even upgrade your
entire system. Here are the key points that you should know about APT and its configuration:
• The
sources.list
file is the key configuration file for defining package sources (or reposi-
tories that contain packages).
• Debian and Kali use three sections to differentiate packages according to the licenses chosen
by the authors of each work: main contains all packages that fully comply with the
Debian
Free Software Guidelines
9
; non-free contains software that does not (entirely) conform to
the Free Software Guidelines but can nevertheless be distributed without restrictions; and
contrib (contributions) includes open source software that cannot function without some
non-free elements.
• Kali maintains several repositories including: kali-rolling, which is the main repository for
end-users and should always contain installable and recent packages; and kali-dev, which is
used by Kali developers and is not for public use.
• When working with APT, you should first download the list of currently-available packages
with
apt update
.
• You can add a package to the system with a simple
apt install package
. APT will auto-
matically install the necessary dependencies.
• To remove a package use
apt remove package
. It will also remove the reverse dependen-
cies of the package (i.e. packages that depend on the package to be removed).
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• To remove all data associated with a package, you can “purge” the package with the
apt
purge package
command. Unlike a removal, this will not only remove the package but
also its configuration files and sometimes the associated user data.
We recommend regular upgrades to install the latest security updates. To upgrade, use
apt
update
followed by either
apt upgrade
,
apt-get upgrade
, or
aptitude safe-upgrade
. These
commands look for installed packages that can be upgraded without removing any packages.
For more important upgrades, such as major version upgrades, use
apt full-upgrade
. With this
instruction,
apt
will complete the upgrade even if it has to remove some obsolete packages or
install new dependencies. This is also the command that you should use for regular upgrades of
your Kali Rolling system. Review the pros and cons of updates we outlined in this chapter.
Several tools can be used to inspect Debian packages:
•
dpkg --listfiles
package (or -L) lists the files that were installed by the specified package.
•
dpkg --search file
(or -S) finds any packages containing the file or path passed in the
argument.
•
dpkg --list
(or -l) displays the list of packages known to the system and their installation
status.
•
dpkg --contents file.deb
(or -c) lists all the files in a particular
.deb
file.
•
dpkg --info file.deb
(or -I) displays the headers of the specified
.deb
file.
• The various
apt-cache
subcommands display much of the information stored in APT’s in-
ternal database.
To avoid excessive disk usage, you should regularly sort through
/var/cache/apt/archives/
.
Two commands can be used for this:
apt clean
(or
apt-get clean
) entirely empties the direc-
tory;
apt autoclean
(
apt-get autoclean
) only removes packages that can no longer be down-
loaded because they have disappeared from the mirror and are therefore useless.
aptitude
is an interactive program that can be used in semi-graphical mode on the console. It is
an extremely robust program that can help you install and troubleshoot packages.
synaptic
is a graphical package manager that features a clean and efficient graphical interface.
As an advanced user, you can create files in
/etc/apt/apt.conf.d/
to configure certain aspects
of APT. You can also manage package priorities, track automatically installed packages, work with
several distributions or architectures at once, use cryptographic signatures to validate packages,
and upgrade files using the techniques outlined in this chapter.
In spite of the Debian or Kali maintainers’ best efforts, a system upgrade isn’t always as smooth as
we would hope. When this happens, you can look at the
Kali bug tracker
10
and at the
Debian bug
tracking system
11
at https://bugs.debian.org/
package
to check whether the problem has already
10
https://bugs.kali.org/
11
https://bugs.debian.org/
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Chapter 8 — Debian Package Management
been reported. You can also try to downgrade the package or to debug and repair a failed package
maintainer script.
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